1. Field of the Invention
The present invention relates to a projection lens unit for a projector for enlarging and projecting an image on a screen, and more particularly, to a improved projection lens unit for a projector which can improve aberration characteristics and which can reduce the space occupied by lenses.
2. Description of the Related Art
In general, a projector includes a lamp for generating and irradiating light using halogen or xenon, a transmission or reflection type display device for generating an image by selectively transmitting or reflecting the light irradiated from the lamp, and a projection lens unit for enlarging an image and projecting the same on a screen. A liquid crystal display (LCD) or a micro-mirror device is be employed as the display device.
The projection lens unit must be designed in consideration of optical performance such as vertical and horizontal angle of view, aberration and the like, or space occupied by the lenses in the projector.
Taking this into consideration, the present applicant previously proposed a projection lens unit which is filed on Jan. 24, 1996 in Korean patent application No. 1858 (invented by Dong-ha Kim in the title of Wide View-Angle Liquid Crystal Projection Lens System).
The proposed projection lens unit includes a prism for switching the angle of an optical axis to arrange the optical axis to be bent by 90.degree. or greater, thereby reducing the space occupied in the projector and achieving a wide angle of view.
However, since the respective lens groups have circular shapes, there is a limit in reducing the space occupied thereby.
Also, in "Reflection Type Projecting Apparatus" proposed by the present applicant, U.S. Ser. No. 09/057,585 filed on Apr. 9, 1998, invented by Soon-chul Choi, light is made to be incident or reflected slantingly into or from a ferroelectric liquid crystal device (FLCD) using a critical angle prism to convert the traveling path of the light. Accordingly, in the case where a conventional projection lens unit which is widely known is employed, the light reflected from the FLCD travels slantingly with respect to the optical axis of the projection lens unit, thereby causing deterioration in contrast and aberration characteristics of an image formed on a screen.